1. Field of the Invention
The present invention relates to a secondary air supplying apparatus for an internal combustion engine to introduce air to an exhaust gas purifying catalyst for purpose of exhaust gas purification at a starting time of the internal combustion engine, especially for purpose of reduction of HC, CO, and NO.sub.x, and relates to a gas heating apparatus thereof.
2. Description of the Prior Art
FIG. 1 is a general view of a conventional secondary air supplying apparatus. In the drawing, reference numeral 1 is an internal combustion engine body in communication with an air flow duct 2. The air flow duct 2 includes an air cleaner 3, an air flow sensor 4, a throttle body 5 for gradually releasing an air flow, a surge tank 6 for arranging the air flow, an intake manifold 7, an exhaust manifold 8 through which the air discharged from the internal combustion engine body 1 passes, a catalytic apparatus 9 having a catalyst for purifying the exhaust gas, and an exhaust muffler 10 in this order starting from the intake side toward the exhaust side.
A secondary air supply pipe 11 is provided between the air cleaner 3 and the exhaust manifold 8 in the air flow duct 2 to supply secondary air to the catalytic apparatus 9. In the illustrative embodiment, an air pump 12, a flow control valve 13, and a check valve 13a are mounted in the course of the secondary air supply pipe 11. The air pump 12 and the flow control valve 13 are connected to a control unit 14 which is connected to a detecting apparatus 15 for detecting various conditions.
A description will now be given of the operation. Air passing through the air cleaner 3 or the like, that is, through the air flow duct 2 is sucked into the internal combustion engine body 1 together with fuel. After combustion, an exhaust gas passes through the exhaust manifold 8 to be externally discharged. The exhaust gas in the exhaust manifold 8 contains a large amount of air pollutant such as HC, CO, or NO.sub.x so that the exhaust gas is discharged into the atmosphere after reduction of the air pollutant by the catalytic apparatus 9.
However, at the start time of the internal combustion engine, the exhaust manifold 8 can not supply the catalytic apparatus 9 with air having a temperature to easily react with the catalyst and containing rich oxygen, resulting in insufficient purification of the exhaust gas. Hence, it is necessary to supply an external air through the secondary air supply pipe 11.
In the illustrative embodiment, the secondary air is forcedly supplied into the exhaust manifold 8 through the air pump 12 mounted in the course of the secondary air supply pipe 11. The control unit 14 decides depending upon data detected by the detecting apparatus 15 such as a water temperature, revolution, boost, or pump pressure. Subsequently, indication from the control unit 14 controls the revolution or the like of the air pump 12 to supply an appropriate amount of air to the upstream of the catalytic apparatus 9. Further, in the illustrative embodiment, the indication from the control unit 14 can adjust divergence of the flow control valve 13 so as to optimize a feed rate of the secondary air.
However, in the secondary air supplying apparatus, low-temperature external air is fed into the catalytic apparatus 9 at a low-temperature starting time so that the catalyst can not smoothly react due to the low temperature. Consequently, there is a problem in that the reaction in the catalytic apparatus 9 can not be promoted effectively.
In order to overcome the problem, there has been proposed a preheating apparatus disclosed in, for example, Japanese Patent Publication (kokai) No. 55-29003. As shown in FIG. 1, the preheating apparatus 16 is attached to the exhaust manifold 8 and is connected to the secondary air supply pipe 11.
The preheating apparatus transfers preheat from the exhaust gas in the exhaust manifold 8 to heat the secondary air in the secondary air supply pipe 11, thereby reducing a decrease in a temperature of a mixed gas of the exhaust gas supplied to the upstream of the catalytic apparatus 9 and the secondary air so as to promote a reaction speed in the catalytic apparatus 9.
In an alternative embodiment, the secondary air is introduced by making use of negative pressure of the exhaust manifold 8 without the air pump 12 in the course of the secondary air supply pipe 11 and the control unit 14 for controlling the air pump 12. FIG. 2 is a general view of a secondary air supplying apparatus of this kind disclosed in, for example, Japanese Utility Model Publication (Kokoku) No. 3-2663. In FIG. 2, reference numeral 11a means a secondary air supply pipe, and 11b is a lead valve mounted on the upstream of the secondary air supply pipe 11a.
The secondary air supplying apparatus utilizes a variation in exhaust pressure caused by intake and exhaust process in the internal combustion engine body 1. That is, the secondary air is introduced by opening the lead valve 11b provided for the secondary air supply pipe 11a in case of the negative pressure in the exhaust manifold 8, and the lead valve 11b is closed to prevent a counter-flow of the exhaust gas in case of positive pressure in the exhaust manifold 8.
The conventional secondary air supplying apparatus for the internal combustion engine is provided as set forth above. Therefore, in either case, it is impossible to stably supply the secondary air having a preferable temperature to the catalytic apparatus 9. Accordingly, the catalytic apparatus 9 can not provide a sufficient effect of the exhaust gas purification, and can not significantly contribute to prevention of air pollution which has been increasingly strongly desired in view of environmental protection in recent years.
That is, the one apparatus described referring to FIG. 1 (which is disclosed in Japanese Patent Publication (Kokai) No. 29003 or the like) makes use of the preheat from the exhaust manifold 8, and can not increase the secondary air temperature sufficiently at the low-temperature starting time at which the exhaust manifold 8 is not hot yet, resulting in insufficient promotion of the reaction in the catalytic apparatus 9.
Further, in the other apparatus discussed referring to FIG. 2 (which is disclosed in Japanese Utility Model Publication No. 3-2663 or the like), the secondary air can automatically be introduced only in case of the negative pressure in the exhaust manifold 8. Hence, it is impossible to stably supply sufficient air required for reduction of the air pollutant such as HC, CO, or NO.sub.x, resulting in a little effect in the exhaust gas purification. In addition, it is necessary to supply the secondary air at the low-temperature starting time at which the catalytic apparatus can not exhibit its true performance. However, a problem remains that catalyst purification efficiency is deteriorated because the exhaust gas temperature decreases when low-temperature air is excessively supplied.